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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>PNG Support: Cairo: A Vector Graphics Library</title>
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<div class="refentry">
<a name="cairo-PNG-Support"></a><div class="titlepage"></div>
<div class="refnamediv"><table width="100%"><tr>
<td valign="top">
<h2><span class="refentrytitle"><a name="cairo-PNG-Support.top_of_page"></a>PNG Support</span></h2>
<p>PNG Support — Reading and writing PNG images</p>
</td>
<td class="gallery_image" valign="top" align="right"></td>
</tr></table></div>
<div class="refsect1">
<a name="cairo-PNG-Support.functions"></a><h2>Functions</h2>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="functions_return">
<col class="functions_name">
</colgroup>
<tbody>
<tr>
<td class="function_type">
<a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> *
</td>
<td class="function_name">
<a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png" title="cairo_image_surface_create_from_png ()">cairo_image_surface_create_from_png</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
</td>
<td class="function_name">
<span class="c_punctuation">(</span><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()">*cairo_read_func_t</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> *
</td>
<td class="function_name">
<a class="link" href="cairo-PNG-Support.html#cairo-image-surface-create-from-png-stream" title="cairo_image_surface_create_from_png_stream ()">cairo_image_surface_create_from_png_stream</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
</td>
<td class="function_name">
<a class="link" href="cairo-PNG-Support.html#cairo-surface-write-to-png" title="cairo_surface_write_to_png ()">cairo_surface_write_to_png</a> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
</td>
<td class="function_name">
<span class="c_punctuation">(</span><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()">*cairo_write_func_t</a><span class="c_punctuation">)</span> <span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="function_type">
<a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
</td>
<td class="function_name">
<a class="link" href="cairo-PNG-Support.html#cairo-surface-write-to-png-stream" title="cairo_surface_write_to_png_stream ()">cairo_surface_write_to_png_stream</a> <span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="cairo-PNG-Support.other"></a><h2>Types and Values</h2>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="name">
<col class="description">
</colgroup>
<tbody><tr>
<td class="define_keyword">#define</td>
<td class="function_name"><a class="link" href="cairo-PNG-Support.html#CAIRO-HAS-PNG-FUNCTIONS:CAPS" title="CAIRO_HAS_PNG_FUNCTIONS">CAIRO_HAS_PNG_FUNCTIONS</a></td>
</tr></tbody>
</table></div>
</div>
<div class="refsect1">
<a name="cairo-PNG-Support.description"></a><h2>Description</h2>
<p>The PNG functions allow reading PNG images into image surfaces, and writing
any surface to a PNG file.</p>
<p>It is a toy API. It only offers very simple support for reading and
writing PNG files, which is sufficient for testing and
demonstration purposes. Applications which need more control over
the generated PNG file should access the pixel data directly, using
<a class="link" href="cairo-Image-Surfaces.html#cairo-image-surface-get-data" title="cairo_image_surface_get_data ()"><code class="function">cairo_image_surface_get_data()</code></a> or a backend-specific access
function, and process it with another library, e.g. gdk-pixbuf or
libpng.</p>
</div>
<div class="refsect1">
<a name="cairo-PNG-Support.functions_details"></a><h2>Functions</h2>
<div class="refsect2">
<a name="cairo-image-surface-create-from-png"></a><h3>cairo_image_surface_create_from_png ()</h3>
<pre class="programlisting"><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> *
cairo_image_surface_create_from_png (<em class="parameter"><code>const <span class="type">char</span> *filename</code></em>);</pre>
<p>Creates a new image surface and initializes the contents to the
given PNG file.</p>
<div class="refsect3">
<a name="cairo-image-surface-create-from-png.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>filename</p></td>
<td class="parameter_description"><p>name of PNG file to load. On Windows this filename
is encoded in UTF-8.</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-image-surface-create-from-png.returns"></a><h4>Returns</h4>
<p> a new <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> initialized with the contents
of the PNG file, or a "nil" surface if any error occurred. A nil
surface can be checked for with cairo_surface_status(surface) which
may return one of the following values:</p>
<p><a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a>
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-FILE-NOT-FOUND:CAPS"><code class="literal">CAIRO_STATUS_FILE_NOT_FOUND</code></a>
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a>
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a></p>
<p>Alternatively, you can allow errors to propagate through the drawing
operations and check the status on the context upon completion
using <a class="link" href="cairo-cairo-t.html#cairo-status" title="cairo_status ()"><code class="function">cairo_status()</code></a>.</p>
</div>
<p class="since">Since: 1.0</p>
</div>
<hr>
<div class="refsect2">
<a name="cairo-read-func-t"></a><h3>cairo_read_func_t ()</h3>
<pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
<span class="c_punctuation">(</span>*cairo_read_func_t<span class="c_punctuation">)</span> (<em class="parameter"><code><span class="type">void</span> *closure</code></em>,
<em class="parameter"><code>unsigned <span class="type">char</span> *data</code></em>,
<em class="parameter"><code>unsigned <span class="type">int</span> length</code></em>);</pre>
<p><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()"><span class="type">cairo_read_func_t</span></a> is the type of function which is called when a
backend needs to read data from an input stream. It is passed the
closure which was specified by the user at the time the read
function was registered, the buffer to read the data into and the
length of the data in bytes. The read function should return
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if all the data was successfully read,
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a> otherwise.</p>
<div class="refsect3">
<a name="cairo-read-func-t.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>closure</p></td>
<td class="parameter_description"><p>the input closure</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>data</p></td>
<td class="parameter_description"><p>the buffer into which to read the data</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>length</p></td>
<td class="parameter_description"><p>the amount of data to read</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-read-func-t.returns"></a><h4>Returns</h4>
<p> the status code of the read operation</p>
</div>
<p class="since">Since: 1.0</p>
</div>
<hr>
<div class="refsect2">
<a name="cairo-image-surface-create-from-png-stream"></a><h3>cairo_image_surface_create_from_png_stream ()</h3>
<pre class="programlisting"><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="returnvalue">cairo_surface_t</span></a> *
cairo_image_surface_create_from_png_stream
(<em class="parameter"><code><a class="link" href="cairo-PNG-Support.html#cairo-read-func-t" title="cairo_read_func_t ()"><span class="type">cairo_read_func_t</span></a> read_func</code></em>,
<em class="parameter"><code><span class="type">void</span> *closure</code></em>);</pre>
<p>Creates a new image surface from PNG data read incrementally
via the <em class="parameter"><code>read_func</code></em>
function.</p>
<div class="refsect3">
<a name="cairo-image-surface-create-from-png-stream.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>read_func</p></td>
<td class="parameter_description"><p>function called to read the data of the file</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>closure</p></td>
<td class="parameter_description"><p>data to pass to <em class="parameter"><code>read_func</code></em>
.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-image-surface-create-from-png-stream.returns"></a><h4>Returns</h4>
<p> a new <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> initialized with the contents
of the PNG file or a "nil" surface if the data read is not a valid PNG image
or memory could not be allocated for the operation. A nil
surface can be checked for with cairo_surface_status(surface) which
may return one of the following values:</p>
<p><a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a>
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-READ-ERROR:CAPS"><code class="literal">CAIRO_STATUS_READ_ERROR</code></a>
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a></p>
<p>Alternatively, you can allow errors to propagate through the drawing
operations and check the status on the context upon completion
using <a class="link" href="cairo-cairo-t.html#cairo-status" title="cairo_status ()"><code class="function">cairo_status()</code></a>.</p>
</div>
<p class="since">Since: 1.0</p>
</div>
<hr>
<div class="refsect2">
<a name="cairo-surface-write-to-png"></a><h3>cairo_surface_write_to_png ()</h3>
<pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
cairo_surface_write_to_png (<em class="parameter"><code><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> *surface</code></em>,
<em class="parameter"><code>const <span class="type">char</span> *filename</code></em>);</pre>
<p>Writes the contents of <em class="parameter"><code>surface</code></em>
to a new file <em class="parameter"><code>filename</code></em>
as a PNG
image.</p>
<div class="refsect3">
<a name="cairo-surface-write-to-png.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>surface</p></td>
<td class="parameter_description"><p>a <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> with pixel contents</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>filename</p></td>
<td class="parameter_description"><p>the name of a file to write to; on Windows this filename
is encoded in UTF-8.</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-surface-write-to-png.returns"></a><h4>Returns</h4>
<p> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if the PNG file was written
successfully. Otherwise, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> if memory could not
be allocated for the operation or
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><code class="literal">CAIRO_STATUS_SURFACE_TYPE_MISMATCH</code></a> if the surface does not have
pixel contents, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-WRITE-ERROR:CAPS"><code class="literal">CAIRO_STATUS_WRITE_ERROR</code></a> if an I/O error occurs
while attempting to write the file, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a> if libpng
returned an error.</p>
</div>
<p class="since">Since: 1.0</p>
</div>
<hr>
<div class="refsect2">
<a name="cairo-write-func-t"></a><h3>cairo_write_func_t ()</h3>
<pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
<span class="c_punctuation">(</span>*cairo_write_func_t<span class="c_punctuation">)</span> (<em class="parameter"><code><span class="type">void</span> *closure</code></em>,
<em class="parameter"><code>const unsigned <span class="type">char</span> *data</code></em>,
<em class="parameter"><code>unsigned <span class="type">int</span> length</code></em>);</pre>
<p><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a> is the type of function which is called when a
backend needs to write data to an output stream. It is passed the
closure which was specified by the user at the time the write
function was registered, the data to write and the length of the
data in bytes. The write function should return
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if all the data was successfully written,
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-WRITE-ERROR:CAPS"><code class="literal">CAIRO_STATUS_WRITE_ERROR</code></a> otherwise.</p>
<div class="refsect3">
<a name="cairo-write-func-t.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>closure</p></td>
<td class="parameter_description"><p>the output closure</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>data</p></td>
<td class="parameter_description"><p>the buffer containing the data to write</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>length</p></td>
<td class="parameter_description"><p>the amount of data to write</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-write-func-t.returns"></a><h4>Returns</h4>
<p> the status code of the write operation</p>
</div>
<p class="since">Since: 1.0</p>
</div>
<hr>
<div class="refsect2">
<a name="cairo-surface-write-to-png-stream"></a><h3>cairo_surface_write_to_png_stream ()</h3>
<pre class="programlisting"><a class="link" href="cairo-Error-handling.html#cairo-status-t" title="enum cairo_status_t"><span class="returnvalue">cairo_status_t</span></a>
cairo_surface_write_to_png_stream (<em class="parameter"><code><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> *surface</code></em>,
<em class="parameter"><code><a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a> write_func</code></em>,
<em class="parameter"><code><span class="type">void</span> *closure</code></em>);</pre>
<p>Writes the image surface to the write function.</p>
<div class="refsect3">
<a name="cairo-surface-write-to-png-stream.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody>
<tr>
<td class="parameter_name"><p>surface</p></td>
<td class="parameter_description"><p>a <a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a> with pixel contents</p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>write_func</p></td>
<td class="parameter_description"><p>a <a class="link" href="cairo-PNG-Support.html#cairo-write-func-t" title="cairo_write_func_t ()"><span class="type">cairo_write_func_t</span></a></p></td>
<td class="parameter_annotations"> </td>
</tr>
<tr>
<td class="parameter_name"><p>closure</p></td>
<td class="parameter_description"><p>closure data for the write function</p></td>
<td class="parameter_annotations"> </td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect3">
<a name="cairo-surface-write-to-png-stream.returns"></a><h4>Returns</h4>
<p> <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SUCCESS:CAPS"><code class="literal">CAIRO_STATUS_SUCCESS</code></a> if the PNG file was written
successfully. Otherwise, <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-NO-MEMORY:CAPS"><code class="literal">CAIRO_STATUS_NO_MEMORY</code></a> is returned if
memory could not be allocated for the operation,
<a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-SURFACE-TYPE-MISMATCH:CAPS"><code class="literal">CAIRO_STATUS_SURFACE_TYPE_MISMATCH</code></a> if the surface does not have
pixel contents, or <a class="link" href="cairo-Error-handling.html#CAIRO-STATUS-PNG-ERROR:CAPS"><code class="literal">CAIRO_STATUS_PNG_ERROR</code></a> if libpng
returned an error.</p>
</div>
<p class="since">Since: 1.0</p>
</div>
</div>
<div class="refsect1">
<a name="cairo-PNG-Support.other_details"></a><h2>Types and Values</h2>
<div class="refsect2">
<a name="CAIRO-HAS-PNG-FUNCTIONS:CAPS"></a><h3>CAIRO_HAS_PNG_FUNCTIONS</h3>
<pre class="programlisting">#define CAIRO_HAS_PNG_FUNCTIONS 1
</pre>
<p>Defined if the PNG functions are available.
This macro can be used to conditionally compile code using the cairo
PNG functions.</p>
<p class="since">Since: 1.0</p>
</div>
</div>
<div class="refsect1">
<a name="cairo-PNG-Support.see-also"></a><h2>See Also</h2>
<p><a class="link" href="cairo-cairo-surface-t.html#cairo-surface-t" title="cairo_surface_t"><span class="type">cairo_surface_t</span></a></p>
</div>
</div>
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